This invention relates generally to antennas and particularly to an antenna of the type tunable over the high frequency (HF) ranges, 3.5 to 30 MHz, such as are used with mobile or fixed radio stations.
Such antennas are well known in the art. They usually include a helically wound resonator mounted on a whip-type antenna. These antennas are frequently used with automobiles for either transmitting or receiving on an amateur frequency band. However, these conventional antennas cannot be utilized as multiband antennas. While the resonator of such antennas is tunable, it cannot be reset to a precise frequency without considerable guesswork.
The resonator of such prior art antennas is quite large in diameter and provides a substantial wind resistance. For this and other reasons, the antenna is usually spring-mounted at the base so that the entire structure can whip back and forth over the car body. This causes a varying distributed capacitance, which in turn will affect the tuning.
It is therefore an object of the present invention to provide a short and efficient antenna for the purpose discussed, which has a relatively small diameter and hence, less wind resistance.
Another object of the invention is to provide a logging scale between movable parts of the antenna to facilitate tuning of the resonator to a particular frequency.
A further object of the present invention is to provide an antenna assembly which is capable of responding to a plurality of frequency bands.